This invention relates to a hydraulically actuated fail-close control choke used in the production of oil and gas wells. Prior control chokes have a flow cage or flow sleeve disposed within a choke body for throttling the flow through the choke to obtain a desired flow rate. Typically these control chokes have used positioning means such as a handwheel operated travelling nut assembly or a hydraulic stepping actuator to control the position of the flow sleeve. In either case, in a sudden emergency when it was imperative to shut off flow through the control choke, valuable time was lost as the travelling nut assembly or stepping actuator took considerable time in closing the control choke. Additionally, often the flow sleeve and control choke were constructed in such a manner to require the positioning means to move the flow sleeve against the pressure in the choke. This arrangement required a larger positioning means thereby adding considerably to the cost of these prior control chokes. The present invention concerns a novel arrangement of flow sleeve and positioning means to reduce the size of the components required and allow an immediate closing of the control choke in emergency situations.
R. R. Crookston U.S. Pat. No. 2,733,041 discloses a plug type valve in which a hydraulically controlled piston in combination with a coil spring biasing means is used to open and close the valve. A handwheel operated stem extends through the piston to allow the plug to be opened or closed independently of the piston.
W. G. Boyle U.S. Pat. No. 3,378,224 is an example of a gate valve with a single acting hydraulic piston cooperating with a spring for reciprocating the gate between open and closed positions. A handwheel operated stem which does not have to overcome the spring load is provided for moving the gate should the piston fail to operate.
J. M. Sheesley U.S. Pat. No. 3,628,397 discloses a valve actuator having a single acting hydraulic piston with a ball nut secured thereto in combination with a spring. A ball shaft is secured to the top of the actuator housing and mounted so its rotation causes movement of the piston and the valve gate which is connected to an extension of the lower portion of the piston.
J. C. Lemmon U.S. Pat. No. 4,167,262 is an example of a pilot actuated valve utilizing a cage with longitudinal slots as the flow controlling member. A partial balancing of the load on the fluid actuator is achieved by allowing the flow to act on the end of the cage. No manual override means is disclosed.
P. R. Orum et al. U.S. Pat. No. 4,213,480 discloses a manual override for a hydraulic actuator of a subsea gate valve. Hydraulic pressure in the actuator normally holds the gate open with a spring therein moving the gate to a closed position in case of malfunction. The override comprises a drive nut threaded onto the valve stem and a drive sleeve telescopically engaging the drive nut and connected by a series of splines. The drive sleeve presents a hex shaped external surface for turning by a wrench. This rotation causes axial movement of the gate when an overriding of the actuator is required.
G. S. Baker U.S. Pat. No. 4,844,407 discloses another override mechanism for a gate valve in which the override stem is threaded through the piston of the hydraulic actuator. A plurality of pins and slots prevent rotary movement of the actuator piston and allow rotation of the override stem to cause movement of the valve gate to an open or closed position independent of the actuator.